1. Field of the Invention
The present invention relates to a thermoelectric module used in, for example, a temperature controller for a semiconductor device and a method of assembling the thermoelectric module in a radiating member.
2. Description of the Related Art
For example, a thermoelectric module used in a temperature controller for maintaining a constant temperature of a laser diode is shown in FIGS. 10 and 11. The thermoelectric module shown in those figures is designed such that a plurality of lower electrodes 4 formed on a lower substrate 2 and a plurality of upper electrodes 5 formed on an upper substrate 3 are bonded to the respective end portions of a plurality of thermoelectric semiconductor chips 6 through first solder. The plurality of thermoelectric semiconductor chips 6 thus structured are connected in series to each other through the plurality of electrodes 4 and 5, and the respective lower electrodes 4 bonded to both end ones of those thermoelectric semiconductor chips 6, thus connected in series to each other, are soldered to corresponding lead wires 9. The lower substrate 2 and the upper substrate 3 are substantially identical in the dimensional configuration with each other. A lower surface of the lower substrate 2 is thickly covered with second solder 7 in advance, and an upper surface of the upper substrate 3 is thickly covered with third solder 8 in advance. The liquidus temperature of the second solder 7 (melting point in case of eutectic solder) is set to be lower than the solidus temperature of the first solder (melting point in case of eutectic solder), and the liquidus temperature of the third solder 8 is set to be lower than the solidus temperature of the second solder 7.
The thermoelectric module 1 is used in a state where the lower substrate 2 is bonded and assembled to a butterfly package (radiating member) B through the second solder 7 (refer to FIGS. 12 and 13), and an endothermic member (for example, a semiconductor device) not shown is bonded onto the upper substrate 3 through the third solder 8. In order to satisfactorily exhibit the performance of the thermoelectric module 1, it is necessary to reduce heat resistances between the endothermic and radiating members and the respective substrates 2, 3, particularly, a heat resistance between the lower substrate 2 and the butterfly package B as much as possible. To achieve this, up to now, the thermoelectric module 1 is mounted on the butterfly package B that has been heated to a slightly higher temperature than the liquidus temperature of the second solder 7 through the second solder 7 and the lower substrate 2 as shown in FIGS. 12 and 13, and side center portions of the upper substrate 3 are held between a pair of support arms A. After the second solder 7 is melted by a heat transmitted from the butterfly package B, the lower substrate 2 is pushed toward the butterfly package B under pressure while being rocked horizontally. This process allows foreign material such as air bubbles or dust to be removed from the interior of the melted second solder 7, and the second solder 7 to be thinned and uniformed in thickness, thereby enabling a reduction in the heat resistance between the lower substrate 2 and the butterfly package B.
In order to facilitate the soldering of the lead wires 9 to the lower electrodes 4, as shown in FIGS. 14 and 15, another conventional thermoelectric module is equipped with a protrusion 2a that protrudes relative to the upper substrate 3 at a side of the lower substrate 2A where the lead wires 9 are drawn (thermoelectric module 1).
In the above-mentioned related art that holds the upper substrate 3 between the paired support arms A to bond the lower substrate 2 onto the butterfly package B, since a force that is exerted on the lower substrate 2 from the support arms A is transmitted through the thermoelectric semiconductor chips 6, the force is exerted on bonding portions of the semiconductor chips 6 and the lower and upper electrodes 4 and 5 through the first solder 1. Therefore, when the liquidus temperature of the second solder 7 and the solidus temperature of the first solder 1 are close to each other, since strengths of the bonding portions of the thermoelectric semiconductor chips 6 and the lower and upper electrodes 4, 5 through the first solder 1 are deteriorated, there arises such a problem that the bonding portions are partially broken due to the above-mentioned force with the result that the thermoelectric module 1 may be broken.
As a manner for solving the above problem, there has been proposed that, in the above-mentioned thermoelectric module 1A structured as shown in FIGS. 14 and 15, a center portion of the protrusion 2a of the lower substrate 2A where no lead wires 9 is disposed is pushed by a single support arm A under pressure and horizontally rocked to bond the lower substrate 2A of the thermoelectric module 1A to the butterfly package B through the second solder 7A. However, in this example, since the lower substrate 2A must be pushed under pressure from only one end portion of the lower substrate 2A by the support arm A, an opposite side of the lower substrate 2A floats up, and foreign material such as air bubbles or dust is incompletely removed from the interior of the melted second solder 7A with the result that the second solder 7A cannot be thinned and uniformed in thickness. Therefore, a heat resistance between the lower substrate 2A and the butterfly package B cannot be satisfactorily reduced.
The present invention has been made to solve the above-mentioned problems with the related art, and therefore an object of this invention is to provide a thermoelectric module and a method of assembling the thermoelectric module in a radiating member, which can prevent bonding portions of thermoelectric semiconductor chips and electrodes from being broken.
Another object of this invention is to provide a thermoelectric module and a method of assembling the thermoelectric module in a radiating member, which can satisfactorily reduce a heat resistance between a lower substrate and a butterfly package.
To achieve the above objects, according to a first aspect of this invention, there is provided a thermoelectric module, comprising: a plurality of thermoelectric semiconductor chips; first and second substrates; a plurality of first and second electrodes formed on said first and second substrates, respectively; and a first solder through which said first and second electrodes are bonded to respective end portions of said thermoelectric semiconductor chips in order to connect the plural thermoelectric semiconductor chips in series, said first substrate being made to include at least two protrusions that protrude toward opposite sides which appear upon at-a-right-angle projection of the second substrate onto the first substrate.
In the thermoelectric module according to this invention, it is preferable that concave portions, convex portions or aperture portions may be formed in the protrusions of said first substrate.
Also, according to a second aspect of this invention, there is provided a method of assembling a thermoelectric module in a radiating member, comprising the steps of: mounting the first substrate of the thermoelectric module according the first aspect of the invention on a radiating member through the second solder having a liquidus temperature lower than a solidus temperature of the first solder; holding the respective protrusions of the first substrate by leading edges of corresponding support arms in a state where the second solder is melted, and pushing the first substrate toward the radiating member under pressure while rocking the first substrate in a direction orthogonal to the pushing direction.
In the method of assembling the thermoelectric module in the radiating member according to this invention, it is preferable that the leading edges of the support arms are engaged with the concave portions, the convex portions or the aperture portions of the respective protrusions, and the first substrate is pushed under pressure and rocked by the support arms.
Also, in the method of assembling the thermoelectric module in the radiating member according to this invention, it is preferable that a temperature difference between a liquidus temperature of the second solder and a solidus temperature of the first solder is set to be lower than 40xc2x0 C.